1. Field of the Invention
The present invention relates to a chair, more particularly to a chair with a stopping device for preventing tilting of a seat relative to a leg unit.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional chair 1 is shown to include a leg unit 11, a base frame 13, a top frame 14, a backrest-supporting frame 15, and a positioning unit 2.
As illustrated, the base frame 13 has opposite front and rear ends, a bottom plate 132 mounted securely on the leg unit 11, and two side plates 131 extending upwardly from two opposite sides of the bottom plate 132. The top frame 14 is disposed above the base frame 13, and includes a seat-supporting plate 142, and two side plates 141 that extend downwardly from two opposite sides of the seat-supporting plate 142 and that are pivoted respectively to the side plates 131 of the base frame 13 through a first pivot 16 so as to permit pivotal action the top frame 14 relative to the base frame 13. A cushion seat 120 is mounted on the seat-supporting plate 142 of the top frame 14. An urging mechanism 19 is mounted on the base frame 13, and urges the front end of the bottom plate 132 toward the top frame 14.
The backrest-supporting frame 15 is disposed rearwardly of the base frame 13, and includes two side plates 151 pivoted respectively to the side plates 131 of the base frame 13 through a second pivot 18, and to two lugs 143 formed on the side plates 141 of the top frame 14 through a third pivot 17 such that the second and third pivots 18, 17 are disposed rearwardly of and are parallel to the first pivot 16. A backrest 10 can be mounted on the backrest-supporting frame 15.
The positioning unit 2 includes a control rod 22 and a stopping member 21 that has a tubular portion 212 defining a retention hole 213 and an annular flange 211 extending radially and outwardly from the tubular portion 212 and welded to an inner one of the side plates 141 of the top frame 14. The control rod 22 extends slidably through two holes 133 in the side plates 131 of the base frame 13, and is movable between a locking position, in which an engaging end 223 of the control rod 22 engages the retention hole 213 in the stopping member 21 so as to prevent the top frame 14 from tilting relative to the base frame 13, and a releasing position, in which the engaging end 223 of the control rod 22 disengages the stopping member 21 so as to permit tilting of the top frame 14 relative to the base frame 13.
Disadvantages of the conventional chair reside in that welding of the stopping member 21 to the inner side plate 141 of the top frame 14 is difficult to conduct, and that alignment of the retention hole 213 with the holes 133 is not easy. Moreover, since the diameter of the holes 133 is required to be approximate to that of the control rod 22, operation of the control rod 22 to extend the engaging end 223 into the retention hole 213 is not smooth. Besides, the engaging end 223 of the control rod 22 tends to deform after a period of use.